Protective circuit for transformerrectifier systems



R. 0. WHITESELL ETAL 2,386,526 PROTECTIVE CIRCUIT FOR TRANSFORMER-RECTIFIER SYSTEMS Filed Sept. 9, 1943 IN VEN TORS @79pm .fd/Jam.,

Patented Oct. 9, 1945 PROTECTIVE CIRCUIT Fon TnANsFonMEnnEcTIFIEIt SYSTEMS Robert 0. Whitesell and P apolis, Ind., assignors aul B. Freeman, Indianto P. R.

Mallory & Co.,

Inc., Indianapolis, Ind., a corporation of Delaware Application September 9, 1943, Serial No. 501,602l

2 Claims.

This invention relates to protective circuits for transformer-rectifier systems.

An object of the invention is to improve protective circuits for transformer-rectifier systems using tapped transformers.

Other objects of the invention will be apparent from the description and claims.

In the drawing the figure shows a transformerrectifier system embodying features of the invenon. A

In power supply systems using dry disc rectiflers, such as magnesium-cupric sulfide rectiiiers, selenium rectifiers, copper oxide rectilers and the like it is necessary to protect the rectiflersagainst excessive currents which will damage the rectifying junctions o r develop excessive heat which will do the damage. Heretofore thermostatic devices have been used for breaking the power supply circuit when the rectiflers approach dangerously high temperatures. The thermostatic devices have the disadvantage of slow operation, so that they do not protect the rectiers from sudden overloads of current. Where tapped transformers are used it is desirable to use a circuit breaker in the input line to protect both the transformer and rectiier againstl abnormal current conditions.

Thermal and magnetic type circuit releases have also been used in the primary circuits ci transformers where the current ratio remains practically constant.

On thermostatlc devices in rectifier assemblies the heat rise will not be in proportion to current because back leakage (reverse current losses) vary with input voltage.

However, if the tap positions are changed on the transformer to change the D. C. output voltage then current ratio from the primary to the secondary will also vary. Hence, a current overload device in the primary circuit will not properly protect the rectifier for all transformer settings.

'Ihe present invention embodies a fast operating circuit controlled by the alternating current between the transformer secondary and the rectier to interrupt the power supply to the trans- 4 former primary.

The drawing is a diagram of a protective circuit applied to a transformer-rectiiier system suitable for supplying D. C'. for electric plating, welding, charging or other operations from a 3-phase A. C. supply I0. Tapped transformer I2 is supplied from circuit; III through circuit breaker II. 'I'he transformer has its three primary windings tapped so that the transformer ratio can be varied by adjusting switch contacts I3.

A 3-phase full-wave rectifier I4 is fed from the secondaries of transformer I2 and supplies D. C. at its output terminals I5.

A pair of current transformers I6 and II are located in two of the conductors leading from the transformer to the rectifier. The output of these current transformers is supplied to windings I8 and I9 respectively which control the release of circuit breaker II. Circuit breaker II is preferably of the thermal overload type with a manual reset mechanism. When the current through current transformer I6 or I1 exceeds the safe operating level for rectier I4 the current supplied to winding I8 or I9 will melt a solder link which will trip the release mechanism for the circuit breaker and open the power supply circuit It.

It is contemplated that the circuit breaker may be of other known types such as magnetically tripped devices.

By the present invention the rectiler and transformer are always protected for the same current overload value regardless of the transformer setting.

While specific embodiments of the invention have been described, it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

l. In a transformer-rectiier sysm of the type wherein an A. C. supply circuit feeds an adjustable ratio tapped transformer through a circuit breaker and the transformer feeds a fullwave dry disc rectifier through A. C. secondary circuit conductors and said rectifier supplies D. C. to a pair of output conductors, the combination with at least one oi said secondary circuit conductors of a. current transformer having its output connected to the tripping coil of said circuit breaker.

2. A transformer-rechner system wherein an A. C. supply circuit feeds an adjustable ratio tapped transformer through a circuit breaker and the transformer feeds a full-wave dry disc rectier through A. C. secondary circuit conductors and said rectifier supplies D. C. to a pair of output conductors, characterized by the fact that there is combined with at least one of said secondary circuit conductors a current transformer having its output connected to the tripping coil of said circuit breaker.

ROBERT G. WHITESEIL. PAUL B. FREEMAN. 

